The present invention relates generally to pharmaceutical compositions. More specifically, the present invention relates to premixed ranitidine formulations.
Ranitidine [N-[2-[[[5-(dimethylamino) methyl-2-furanyl] methyl] thio] ethyl]-N'-methyl-2-nitro-1,1-ethenediamine] is a histamine H.sub.2 antagonist that blocks the secretion of gastric acid and is widely used to treat peptic ulcer disease. Oral and parenteral formulations including ranitidine are known.
Typically, pharmaceutical products must be discarded after they degrade to less than 90% potency. One of the problems encountered with ranitidine formulations is that they suffer the disadvantage of degradation during terminal sterilization. This can be compensated for by manufacturing overages, but doing so means that when the product is at 100% potency, it already contains several % degradation.
U.S Pat. No. 4,585,790 ('790 patent) discloses an aqueous based ranitidine formulation that is buffered so that it has a pH in the range of 6.5 to 7.5. Citrate and phosphate salts are used as buffers. The '790 patent states that a buffered ranitidine formulation is particularly stable when compared with a ranitidine formulation having a lower pH. Indeed, the patent states that ". . . the rate of breakdown in ranitidine is about 10 times faster for a solution buffered to a pH of 5.5 than for a solution buffered to pH 7.0. "
Examples of buffered admixed ranitidine formulations and short term stability testing of same are discussed in: Galante et al, Stability of Ranitidine Hydrochloride at Dilute Concentration in Intravenous Infusion Fluids at Room Temperature, American Journal of Hospital Pharmacy, Vol. 47, July 1990, pp. 1580-1583; and Lampasona et al, Stability of Ranitidine Admixtures Frozen and Refrigerated in Minibags, American Journal of Hospital Pharmacy, Vol. 43, April 1986, pp. 921-925.
Of course, the addition of a buffer to a formulation increases the cost and time necessary to prepare the formulation. A further disadvantage with respect to a formulation such as that disclosed in the '790 patent, is that during sterilization of the formulation, approximately 4 to 8% of the ranitidine degrades.